Radio receiving system



May 15,1928. 1,669,959

P. J. WALSH RADIO RECEIVING $YSTEM Filed Feb. 23, 1926 2 Sheets-Sheet 1 P/l/Y/P J. Wa/sh BY W HIS ATTORNEY May 15, 1928. 1,669,959

P. J. WALSH RADIO RECEIVING SYSTEM 9 Filed Feb. 25, 1926 2 Sheets-Sheet 2 F'IllZ- INVE'N TOR hi/k J WdZsh BY Lu 564W HIS ATTORNEY Patented May 15, 1928.

UNITED STATES PHILIP JOHN WALSH, OF SAN FRANCISCO, CALIFORNIA.

BAIDIO RECEIVING SYSTEM.

Application filed February 23, 1926. Serial No. 89,976.

This invention relates to a system for receiving and amplifying high frequency electrical impulses, such for example as radio signals.

In my Patent No. 1,594,582, issued August 3, 1926, and entitled Amplifier system, I describe a scheme in which several thermionic vacuum tubes are utilized, each having a control electrode and a positive electrode or plate, in addition to the filament that serves as the source of electrons. I explain in that application, the advantages secured by providing a source of constant direct current for impressing a positive voltage upon the plate as regards the filament, which plates are arranged in parallel; and I further disclose a scheme whereby the amplifying effect of the two tubes can be built up and greatly increased.

In the present application, I shall describe several further forms of the invention, based upon substantially the same fundamental principles; and it is accordingly one of the objects of my invention to provide a high degree of amplification with relatively few tubes. I

It is still another object of my invention to make it possible to secure this degreeof amplification without creating instability in the circuits.

My invention possesses many other advantages, and hasother objects which may be made more easily apparent from a consideration of several embodiments of my invention. For this purpose I have shown a fewforms in the drawings accompanying and forming part of the present specification. I

shall now proceed to describe these forms in detail, which illustratethe general principles of my invention; but it-is to be understood that this detailed description is not to be taken in a limiting sense, since the scope of my invention is best defined by the appended claims.

Referring to the drawings:

Fi ure 1 is a schematic wiring diagram of one ormbf my invention; and

Fig. 2 is a diagram of a modification thereof.

In Fig. 1, there is shown an absorbing circuit, such as elevated conductors J1, loading coil 12, and a ground connection 13. In the present instance, there is inductively coupled to coil 12, a tunable circuit 14, comprising a coil 15 in inductive relation with coil 12,

termed the input circuit.

and a variable condenser 16. As is wellunderstood, upon proper tuning as by adj'ustment'of condenser 16, a maximum E. M. F. can be secured for the particular'frequency received, across the terminals of the condenser 16, or of coil 15. This E. M. F. is caused to aflectan electronic emission device 17 directly. I

This device includes a heated filament 18, from which electrons are attracted to a plate 19, kept at a potential positive with respect to the filament in order to attract the electrons. It is well-known that the space current between the plate and filament can be varied by a comparatively large amount by the aid of a control electrode 20, such as a grid, interposed between the plate and filament, and controlling the potential of a point between these two electrodes. It is this theory upon which the amplification b such tubes is based. In order to provi e the proper potential difi'erences between the filament l8 and grid 20, these two electrodes are accordingly connected to opposite terminals of the condenser 16. The circuit thus formed between these electrodes can be aptly In order to heat filament 18, it is connected, through a variable resistance 21, with a source of electrical energy, such as a portion of the battery 22.

Connections 23 and 24 serve as the links be- Broadly this is accomplished in a manner set forth in my prior application. Thus .the

output circuit for tube 17 can be traced from the lower positive terminal of battery 22,

connection 26, coils 27 and 28, variable ta 29 on a resistor 30, through a portion of sai resistor, coil 31, plate 19, back to filament 18, and by way of connection 23, to the other terminal of battery 22. The coil 27 can be an iron cored coil, forming with coil 28, an effective radio frequency choke, of such value that the supply of, direct current in the path just traced is maintained constant.

The space current fluctuations must therefore find another path distinct from the battery 22. This is accomplished by connecting, in parallel with the output circuit of tube 17, the output circuit of the tube 25. This tube has a filament 32 also heated fromv battery 22, as well as the plate electrode 33. The output circuit can therefore be traced in common with that of tube 17 up to tap 29, where it continues through a portion of resistor 30, coil 33 in close inductive relation with coil 31 and opposed thereto, plate 33, filament 32, back to battery 22. It is thus seen that whatever fluctuations may be set up in the space current of tube 17 causes equal and opposite fluctuations in the space current of tube 25, for the sum of these space currents must be constant, due to the constancy of the current from source 26.

The tap 29 and resistor 30 are provided in order to adjust the relative impedance of the two space current paths, whereby exact neutralization can be effected between coils 31 and 33 when no signals exist, and there fore, no fluctuations in the space current of tube 17. Resistor 30 can be of the order of 200 ohms.

.tube 17 alone. All this has been described and claimed in the prior application re' ferred to. l

The input circuit of tube 25 is arranged to be affected by this magnetic unbalance be tween coils 31 and 33', whereby large variations in the impedance through tube 25 are alsosecured, in a sense such as to augment the effect of the variations in tube 17 For coils 31 and 33, in which is induced an E. M. F. in accordance with the variations in the unbalanced currents flowing in these coils. In order to tune the oscillations thus set up, a variable condenser 35 is connected across coil 34. One terminal of coil 34 is connected, as by lead-36, with the grid 37 of tube 25. To complete the input circuit for this tube, Intilize a rectifying arran ement for the impulses in coil 34. T is assists not only in stabilizing the system, but also serves to detect the signal.

The rectifier arrangement in thisinstance' is shown as a tube 38, connected between the other terminal of coil 34 and filament 32.

the coil 42, and a variable resistance 43, bridged by a battery'44 having its negative terminal connected to the grid 41.

.It is evident that only those half-cycles of current can pass through tube 38 which make the lower terminal or coil 34 positive; therefore there is a rectifying effect, and grid 37 can be only negatively charged never positivelybecause it is connected to the upper terminal of coil 34, which is negative when the lower terminal is positive. The rectified current through tube 38 finds a return path through high resistance 45 to upper terminal of coil 34.

The imposition of a negative charge on grid 37 of a value dependent upon the degree of unbalance of coils 31 and 33, serves to accentuate this unbalance, and therefore coil 34 responding thereto, can be taken as forming the output circuit for the system thus far explained. But before describing how this coil afiects the succeeding stages, it is advantageous to consider in greater detail the operation of the system thus far set forth. Of course the diagram is purely schematic; coils 12 and 15 can be toroidal, and may be variably coupled together; coils 31, 33', and 34 can be either toroidal or honeycombed, or any other kind of high frequency coil. Furthermore, the negative terminals of all of the filaments can be grounded as is sometimes done, and is indicated at 46." These refinements however, are of course not absolutely essential.

The stabilizing effect of the rectifier tube 38 can be controlled in several ways. For

example, the tap on resistance-43 can be varied, to vary the potential diiferenc'e'between the grid and filament thereof; or the resistance in the circuit of filament 39 can be varied. In either manner, the effective impedance of the tube can be adjusted. For receivthis. purpose, there is a coil 34, coupled to-\ ing long wave signals, the filament 39 can be heated to a higher degree without danger of instability; while short wave signals require a reduced heating. Similarly, if the negative bias system is used for controlling the action of tube 38, then the tap on resistance 43 must be adjusted to give a larger negative bias to the grid when shorter wave lengths are received.

Since only the rectified half-waves are allowed to affect the grid circuitof tube 25, and since the degree to which this rid circuit is affected can be easily controlled, it is evident that it is a simple matter to produce stable operation without the production of parasitic oscillations. The rectification also serves as detection; therefore it is necessary merely to connect succeeding amplifier stages across an element in the circuit in which only the half-wave currents can exist. Such an element is the resistance45, across the terminals of which, an audio frequency amplifier tube '46 can be connected.

This tube has an input circuit, including filament 47 and grid 48 connecting across the resistance 45, and operating in a well-known manner to cause amplified fluctuations in the space current between filament 47 and the positive or plate electrode 49. This tube 46 is paired with anothertube 50, similarly to the arrangement of tubes and 17, whereby fluctuations in tube 46 are caused to produce opposite fluctuations in tube 50. For this purpose, provisions are again made to ensure constant current fiow through the source supplying the output circuits of both tubes. Thus battery 22 has connected in series therewith an impedance 51, between the positive terminal of the battery and a tap 52, where the current divides and passes through both the output circuits of tubes 46 and 50.

The output circuit of tube 46 includes a portion of balancing resistor 53, a coil 54, plate 49, filament 47. back to the negative terminal of battery 22. Similarly, the output circuit of tube 50 includes a portion of effects.

resistor 53, coil 55, bucking coil 54 and on the same iron core 56 therewith, plate 57 of tube 50, filament 58 thereof, back to the negative terminal of battery 22. The core 56 can be used to advantage, because now audio frequency currents are used. This core has a limb 59 on which coil 60 is placed, which is thus responsive to the unbalance in the magnetism produced by coils 54 and 55. This unbalance is in turn used to affect the space current of tube 50, by being connected between the filament 58 and grid 61 thereof. The building up of a magnetic field in the core 56 by the difference in the output circuits is controlled by the aid of a movable armature 62 placed in a gap in the magnetic circuit of core 56 and leg 59.

The telephone 63 is shown as inductively coppled-with coils 54 and 55, by the aid of 0011 64 wound on another leg 65 of core 56. T1118 telephone carries the amplified audio frequency currents which are induced due to the varying unbalance between coils 54 and 55, accentuated by the efl'ect of the grid circuit control of coil 60.

The tubes 17 and 25 and the associated c rcuits can designated as a radio freuency system; while tubes 46 and 50 and t e associated circuitscan be designated as an audio frequency system; the tube 38 serves as a detector. It would of course .be poss ble to multiply such systems indefinitely by proper cascade connections. In Fig. 2, however, I disclose a further scheme for provlding a succession of amplification In this figure, merely for the sake of illustrating the various forms my invention ma take, I show a loop absorbing circuit, inc udin 'a loop 66 having a tunin condenser 6. in series therewith. As efore, the input electrodes 68 and 69 of an amplifier 70 are connected respectively across the terminals of the condenser 67, whereby the space current therethrough is varied. The battery 71 serves as the source of electrical energy for the output circuit for tube 7 0.

the current flow therefrom being maintained constant as in the earlier forms, as by the aid of the iron-cored impedance coil 73.

The output circuit for tube 70 can be traced from the positive terminal of battery 71, coil 73, coil 74, plate 75, filament 68, back to the negative terminal. Closely coupled with coil 74 is an opposing coil 78 which is fed from the same constant current source. Its circuit may be traced as follows: from the positive terminal of battery 71, coil 73, coil 78, adjustable resistance 79, back to the. negative terminal. It is evident that in this form of the invention, the opposed coil 78 is not in circuit with any vacuum tube; instead, a resistance 79 is provided to set the current 'flow at such value through this coil as exactly to neutralize coil 74 when no signals are received.

When signals are received, the current in coil 74-of course fluctuates, and since the current through coil 73 is constant, there is an equal and opposite fluctuation in the current in coil 78. The result is that an E. M. F. is induced in a coil 80, coupled to coils 74 and 78, and tuned by a variable condenser 81. Since the fluctuations in E. M. F. inthis coil are much larger than in either coil 74 or 78, the advantages of my system are apparent. These fluctuations can 1n turn be impressed upon the input circuit of a succeeding amplifier tube 72, having a filamentv 76, a plate 77, and a grid 82. The output circuit of this tube can in turn be connected in a manner entirely similar to that of tube 70: througha coil 83 maintainin the cur-. rent from source 71 constant, an through coil 84 which is opposed by the coil 85 in a circuit branching the output circuit. The effects being identical with those already described, it is considered unnecessary to detail them further.

While of course it is possible to extend the system to include as many tubes such as 70 and 72 in cascade, yet I show the succeeding tubes 86 and 87, which are influenced by the coil 88 coupled to coils 84 and 85, as forming a detecting system. For this purpose, tube 86 is a two-electrode rectlfier tube, havin a filament 89 and a plate 90. Th s plate 1s connected to one terminal of coil 88. the other terminal being connected to grid 91 of tube 87. By controlling the filament temperatures for this tube. it is pos-,

1grid 91, coil 88, plate 90, filament 89, to lament 92 of tube 87. A high resistance 93 of the order of one or two megohms bridges the input electrodes 92 and 91 to permit the current to flow back to the coil 88 during the active half-cycles.

The tube 87 in turn can be used to affect in succession one or more audio frequency amthat includes the phones 98 or other translating device. 7

It is evident that modifications of the 0011 I arrangements could be'utilized. Preferably toroid coils are used for such as 74,- 78 and 80. Furthermore, types of detectors other than those shown in the two forms could be substituted, such as the well-known grid condenser and leak arrangement.

-I claim:

1. In combination, a source of constant direct current, means forming a a pair of paths in parallel supplied by. said source, means responsive to signaling impulses for varying the impedance of one of the paths, means whereby the currents in the two paths are oppositely varied while leaving their sum constant-,a circuit coupled to both paths to cause it to respond to the variations in current flow therein, said circuit further influencing one of said paths to accentuate the difference in impedance of the two paths,

' and an adjustable rectifying device associatj ed with said circuit for controlling the effeet of said circuit on the paths.

2. In combination, a source of constant direct current, means forming a pair of paths in parallel supplied by said source, means responsive to signaling impulses for var ing the impedance'of one only of the paths, means whereby the currents in the two paths are oppositely varied. a circuit coupled to both paths to cause it to respond to the variations in current flow therein, and means for adjusting the current flow in said circuit. a

3. In combination, a source of constant direct current, means forming a pair of paths in parallel supplied by said source.

means responsive to signaling impulses for varying the impedance of one only of the paths, means whereb the currents in the two paths are oppositely varied, a circuit coupled to both paths to cause it to respond to the variations in current flow therein, and an adjustable rectifying device aSsociated with said circuit for controlling the current flow therein. 1

4. In combination, a source of constant direct current, means forming a pair of producing paths in parallel supplied by said source, means responsive to signaling impulses for Varying the impedance of one of the paths,

current flow, and an amplifier conductively connected to said circuit.

5. In combination, a source of constant direct current, means forming a pair of paths in parallel supplied by said source, means responsive to signaling impulses for varying the impedance of one of the paths, means whereby the currents in the two paths are oppositely varied while leaving their sum constant, acircuit coupled to both paths to cause it to respond to the variations in ourrentflow therein, andmeans, comprising resistances in the paths, for adjusting the impedances thereof. ii

6. In combination, a source of constant direct current, an electronic emission device having its space current supplied by said source, means for varying the impedance of said device in response to received impulses, means forming a path fed from said source in parallel with said device, means whereby the impedance of said path is influenced by said device and not by the received impulses, a pair of opposed coils, one in each path, for a combined magnetic effect equivalent to the difference in current flow in the two paths, a resistor connecting the two coils, and a variable tap on said resistor connecting'to the source, for adjusting the relative effects of the coils.

7. In combination, a' source of constant direct current, a pair of electronic emission devices having their space currents supplied by said source, means for varying the impedance of one of said devices in response to received impulses, a circuitresponsive to the difference in the space currents, and influencing the impedance of the other of said devices, and means for adjusting the effect of said circuit, comprising an electronic emission device having means for, adjusting its impedance, and placed in said circuit.

8'. In combination, a source of constant direct current, a pair of paths supplied in parallel from said source, means for varying the impedance of one only of said paths in response to received impulses, a pair of coils, one in each path, a core on which said coils are placed 1n opposedrelation, means responsive to the combined magnetic effect of said coils, and means for varying the reluctance of the core.

9. In combination, a source of constant direct current, a pair of paths supplied in parallel from said source, means for varying the impedance of one of said paths in response to received impulses, a pair of coils, one in each path, a core I1 Wh10h said coils are placed in opposed relation, means whereby the combined magnetic effect of the coils is utilized to vary the impedance of the other path in order to accentuate the difierencc,

and means for varying the reluctance of the core.

10. In combination, a source of constant direct current, a pair of electronic emission devices, the space currents of which are supplied from said source, means for varying the impedance of one of said devices in response to received impulses, a pair of coils,

one in circuit with each ath, a core on which said coils are placed in opposed relation, means whereby the combined magnetic eflt'ect of the coils is utilized to vary the impedance of the other device in order to accentuate the difference in current flow, and means varying the impedance of one of the paths,

means whereby the currents in the two paths are oppositely varied while leaving their sum constant, a circuit coupled to both paths to cause it to respond to the; variations in current flow therein, and means for adjusting the impedance of at least one of said paths.

In testimony whereof I have hereunto set my hand.

PHILIP JOHN WALSH. 

